The speed of a rocket depends on thrust and the rocket's weight. Thrust is a measure of the force generated from propellant combustion ejected from the rear of the rocket and speed at which the propellant is used. Increased thrust, relative to the rocket's weight, results in greater speed.
Specific impulse is the change in momentum per unit mass for rocket fuels. Specific impulse is a measurement of how much push accumulates as the rocket consumes fuel, or, in terms of thrust, is a rough measurement of how fast the rocket ejects propellant. A rocket having a high specific impulse does not require as much fuel because the rocket gets more push per amount of fuel.
Some rocket engines are variable thrust engines. Variable thrust engines do not have a constant thrust. Rockets having a variable thrust engine, therefore, can generate levels of thrust as needed on demand throughout its flight mission. Hence, the rocket has better control and performance than one with constant thrust engines.
While variable thrust engines are capable of generating levels of thrust as needed on demand for a mission or solar system exploration, it is difficult to control the variable amount of fuel required for the desired thrust.
Throttling an engine increases or decreases the amount of thrust. Throttling adjusts the power level of an engine within its target throttleable range, resulting in an adjustment of the amount and mixture of fuel and oxidizer reaching the engine. However, it is very difficult to control the proper mixing and amount of fuel and oxidizer at low power levels. As a result, engines do not have optimum performance for an entire throttleable range and tend to chug which leads to engine and rocket damage. Most variable thrust engines for rockets are therefore designed to operate only within a small target throttleable range.
It is desirable to design fuel injection systems which can achieve the broadest possible target throttleable range and, in particular, which can offer control of an engine at low thrust levels while maintaining an optimum performance. High performance for a wide range of thrust levels is achieved by controlling the injector inlet area while maintaining adequate pressure drop and good mixing of fuel and oxidizer.
Various attempts have been made in the prior art to control the rate of mixing and the structure of the fuel and oxidizer streams that are created when injecting fuel and oxidizer into the combustion chamber. Throttling is the process of adjusting the position of elements within an engine to release propellant into its combustion chamber. Traditionally the throttling of a liquid fuel engine occurs through valves, which adjust the fuel and oxidizer flow. Control of a mixing process is particularly critical to engines.
For example, U.S. Pat. No. 3,726,088 discloses an injection element that varies the rate of fuel into the fuel manifold by increasing and decreasing the area of the inlet slot. However, the variable inlet slot is only one physical means of controlling a mixing interface. Injection elements have many components and geometric characteristics that can theoretically be altered to vary the structure of the fuel and oxidant streams to increase the level of control over the mixing interface.
There is an unmet need in the prior art for a method for determining specific injection area geometries to accommodate specific applications, engines and throttling requirements.